Danaus plexippus, also known as a
Monarch butterfly is probably one of the most popular butterflies. Growing up it
was always such an exciting event to find a caterpillar and then watch it grow
into a beautiful butterfly. The Monarch butterfly is used a lot in classrooms to
teach about life cycles and migration. It is pretty amazing how such a little
insect can fly so far and so fast. They can fly across continents and oceans and
have even been recorded at flying as many as 130 km a day during migration (Grund).
Continue reading the rest of this website to learn more about this fascinating
insect.

It is hard to tell exactly when butterflies evolved but it was somewhere
around 48 million years ago (Monarch Watch). It seems as though butterflies
probably evolved from moths because they share many of the same characteristics.
Butterflies, however, are diurnal meaning they fly during the day and moths are
nocturnal meaning they fly at night. Below is a representation of some of
Danaus plexippus's closest butterfly relatives.

Danaus plexippus have a wide geographical
range. Their range depends on the presence of milkweed plants that they use for
breeding. They range from North and South America, to Hawaii and Australia, and
recently are establishing themselves in Western Europe. They also live in a
variety of biomes. They live in temperate forests and grasslands, in
tropical rainforests and savannas and also in the mountains.

Danaus
plexippus also follows a seasonal migration pattern like birds. In the
spring and summer, Monarch butterflies can be found further north in open
meadows and fields where milkweed is present. Then in the fall, millions of
monarch butterflies begin their long journey to their overwintering sites. These
overwintering sites are located in southern California and central Mexico. The
picture to the left shows thousands of Monarch butterflies overwintering. Some
butterflies fly as many as 3000 miles to these sites. Many
of the overwintering sites for Monarch butterflies are beginning to disappear
because of illegal logging. Luckily, steps have been taken by the American and
Mexican governments to protect these overwintering sites.

But you may be wondering how do these tiny little creatures find their
overwintering sites year after year? This has been debated about a lot and there
are basically two theories that researchers have came up with. One theory is
that since they fly during the day that the Monarch butterflies use the sun as a
compass when traveling to their overwintering sites. This would involve using
the angle of the sun with some sort of internal clock to predict which way was
south. Another theory is that Monarchs like birds use some sort of magnetic
compass to keep them on track. Both ways are still being studied. However, no
matter which way they use; they will always find their way to the overwintering
sites.

Migrations of the Monarch
butterfly are closely watched. In fact there is a very interesting program that
allows students of all ages to be a part of the migration. It is called Journey
North. Students in the Northern United States and in Canada, design colorful
butterflies that are unique to who they are. Then they are sent to students in
areas of Mexico where the Monarch butterflies overwinter. They arrive around the time of the Dia de los
Muertos or the Day of the Dead, which is the same time that the actual
butterflies begin to arrive. According to Mexican legend, these returning
butterflies are thought to carry the ancestors' souls and play a role in the Dia
de los Muertos celebrations (About the Symbolic Monarch Migration). The students
in Mexico then watch over the butterflies until the spring. When the Monarch
butterflies begin to head back, the students in Mexico send the butterflies back
with messages for the students in the north. This unique project allows students
from all over to be a part of this amazing phenomenon.

Touch: Tactile setae
are hairs that extend through a butterfly's exoskeleton and are attached to nerve
cells. Setae play an important role in helping the butterfly sense the relative
position of their body parts. This is especially helpful in flight. Setae is
also located on the butterflies antennae and aid in touch and smell.

Taste: Butterflies
have chemorecptors scattered across their bodies. Chemoreceptors are a lot like
human taste buds. When a chemoreceptor runs into a chemical , it locks it in and
sends a signal to the brain. In monarchs, chemoreceptors are located heavily on
the antennae. Males release a chemical called pheromones and females can
identify this chemical by using chemorecptors. Chemorecptors are also located on
the female's legs. These chemoreceptors are used when the female is trying to
find the right plant to lay its eggs on.

Sight: Adult
butterflies have compound eyes made up of thousands of
ommatidia. Each ommatidia collects light and perceives a picture. This allows
the butterfly to look forwards, backwards and to the sides all at the same time.
They are also able to perceive polarized light. This is also said to maybe aid the
Monarch butterfly in migration.

You do not want to eat me!
Danaus plexippus larvae only feed on milkweed
plants. They eat mostly the leaves of the milkweed plant but if the plant is
populated by many larvae then they will eat other soft parts of the milkweed
plant. The larva’s mouthparts include an upper and lower lip and mandibles. As
an adult, the butterfly uses a straw-like structure called a proboscis to
collect nectar from flowering plants. The picture to the left, shows an adult
Monarch butterfly using its proboscis to collect nectar from a flower.

Even though
Danaus plexippus is able to enjoy great meals, they are not a very
appetizing meal for other predators. Milkweed plants produce glycosides which
are a type of chemical defense that the plants produce to keep away herbivores.
When larvae eat the milkweed, they collect and store these glycosides. This
causes the Monarch butterfly to taste horrible to its predators. Many other
butterflies will actually try to mimic the Monarch butterfly's colors to scare
away predators. One good example of this is the Limenitis archippus, also known as
the Viceroy butterfly. The pictures below are of both a Viceroy butterfly and a
Monarch butterfly. Can you tell which one is which?

The butterfly on
the left is the Viceroy butterfly and the one on the right is the Monarch
butterfly. Birds flying above can not tell the difference between the two
butterflies so they will leave each of them alone. However, the difference
between the two can easily be seen in these two pictures. The Viceroy butterfly
has a black stripe across its two back wings and the Monarch does not.

Danaus plexippus reproduce early
in the spring right before they begin their migration to the north. Monarch
butterflies reproduce sexually and fertilization is internal. The courtship of
Monarch butterflies is a little different than most Lepidoptera because the
males sometimes force the females to copulate with them. Also Danaus
plexippus do not depend on the release of pheromones as much as other
butterflies. Courtship first begins in the air. The aerial phase consists of the
male nudging and eventually tackling the female to the ground. While on the
ground, copulation occurs. The male’s spermatophore is transferred to the
female. Only about 30% of mating attempts at overwintering sites end in
copulation (The Monarch Butterfly, 61). Then once the female reaches the
breeding grounds, she lays the eggs on a milkweed plant.

Monarch butterflies also go through
complete metamorphosis. Complete metamorphosis has four distinct stages. These
stages include: egg, larva, pupa, and adult. The first stage of the life cycle
is the egg. Once the egg is laid on the milkweed plant, it takes anywhere from 3
– 15 days to hatch. The egg then hatches into a larva. The larva feeds on the
milkweed plant and grows into the caterpillar. The caterpillar is yellow, black
and white striped. After about a two week period the caterpillar attaches its
self upside down to a twig. Within a period of about two hours, the caterpillar
will shed its outer skin and form a chrysalis. About two weeks later, the adult
Monarch butterfly will emerge from the chrysalis.

Danaus plexippus
interact with a variety of species. In the larval stage of Danaus plexippus,
the caterpillar uses a milkweed plant as its host plant. The milkweed provides
the larva with food and nutrients for it to grow. Monarch butterflies also have
some predators. Though most predators are driven away because of the awful taste
of Monarch butterflies, some birds, mice, wasps and fire ants still eat them.
The Monarch butterfly adult is least likely to be eaten by predators. During
overwintering, monarch adults do have some avian predators. It is difficult to
tell if the bird is actually a predator or if they are just curious about trying
a Monarch butterfly. The egg and larva stage of a monarch butterfly are the most
dangerous. Wasps tend to collect larvae to feed to their own larvae. Fire ants
also decrease the population of Monarch butterflies in the spring and fall (The
Monarch Butterfly, 47). Danaus plexippus is also used as a host. Monarch
paraitoids include twelve species of tachinid flies and at least one species of
brachonoid wasp (The Monarch Butterfly, 28).